Add VideoRotation UMA Logging

content/renderer/media/webmediaplayer_impl.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/media/webmediaplayer_impl.h"
 
 #include <algorithm>
 #include <limits>
 #include <string>
 #include <vector>
@@ skipping 945 matching lines @@
   // should know when to invalidate themselves http://crbug.com/337015
   InvalidateOnMainThread();
 }
 
 void WebMediaPlayerImpl::OnPipelineMetadata(
     media::PipelineMetadata metadata) {
   DVLOG(1) << __FUNCTION__;
 
   pipeline_metadata_ = metadata;
 
+  UMA_HISTOGRAM_ENUMERATION("Media.VideoRotation",
+                            metadata.video_rotation,
+                            media::VIDEO_ROTATION_MAX + 1);

[Alexei Svitkine (slow), 2014/07/17 18:20:59]

Optional nit:

General convention for UMA histograms is to have the MAX entry be 1 higher than
the last entry, so that the +1 here would be unnecessary (once you update the
enum) and also makes it so you don't need to change what the MAX ='s to each
time you add a new entry.

[scherkus (not reviewing), 2014/07/17 18:51:48]

Us media folk decided a while back that defining _MAX as LAST_VALUE + 1 isn't
technically correct as "max" is typically defined as an inclusive endpoint.
Using something like _NUM (which typically is LAST_VALUE + 1) isn't good either
since over the long run, enum values can get deprecated leaving holes in the
enum, leading to _NUM being misleading. Also, introducing an extra enum for the
sake of UMA pollutes all non-UMA switch/case statements.

So we standardized on _MAX and wrote a PRESUBMIT.py to verify that enums, _MAX,
and UMA usage is correct:
http://src.chromium.org/viewvc/chrome/trunk/src/media/PRESUBMIT.py

   SetReadyState(WebMediaPlayer::ReadyStateHaveMetadata);
 
   if (hasVideo()) {
     DCHECK(!video_weblayer_);
     video_weblayer_.reset(
         new WebLayerImpl(cc::VideoLayer::Create(compositor_)));
     video_weblayer_->setOpaque(opaque_);
     client_->setWebLayer(video_weblayer_.get());
   }
 
@@ skipping 382 matching lines @@
   compositor_task_runner_->PostTask(FROM_HERE,
                                     base::Bind(&GetCurrentFrameAndSignal,
                                                base::Unretained(compositor_),
                                                &video_frame,
                                                &event));
   event.Wait();
   return video_frame;
 }
 
 }  // namespace content